Diffusion vacuum pump apparatus



SePf- 19, 1967 w. G. `acI-ILER ETAL 3,342,405

DIFFUSION VACUUM PUMP APPARATUS Filed Aug. 9, 1965 wmaw om 39 I7 l i|f|.f|.., Z Mmm f1 4f www@ |||||lm- 7 s a Il l N N M ii afi. M ff 1 #mayfw W

United States Patent Ofice 3,342,405 Patented Sept. 19, 1967 3,342,405DIFFUSION VACUUlVI PUMP APPARATUS Werner G. Bchler and Hans `loachimForth, Cologne,

Germany, assignors to Leybeld Holding AG, Zug, Switzerland, a Swissjoint-stock compari Filed Aug. 9, 1965, Ser. No. 478,338 Claimspriority, application Germany, Get. 17, 1964, L 49,051 2 Claims. (Cl.230-101) ABSTRACT F THE DHSCLSURE A four stage diffusion pump includingfour jet assemblies mounted one above the other, each jet assembly beingcircular and having a uniform annular mouth gap. The width of the secondjet assembly mouth gap is 0.9 to 1.3 times the width of the first orbottom jet assembly mouth gap; the width of the third jet assembly mouthgap is 0.5 to 0.9 times the width of the first jet assembly mouth gap;and the width of the fourth or top jet assembly mouth gap is 0.4 to 0.6times the width of the first jet assembly mouth gap. The diameter of thesecond jet assembly mouth gap is 0.88 to 0.92 times the diameter of thefirst jet assembly mouth gap; the diameter of the third jet assemblymouth gap is 0.55 to 0.62 times the diameter of the first jet assemblymouth gap; and the diameter of the fourth jet assembly mouth gap is 0.28to 0.30 times the diameter of the first jet assembly mouth gap. Thedistance between the second and third jet assembly nozzle lips is 1.0 to4.0 times the distance between the first and second jet assembly nozzlelips; and the distance between the third and fourth jet assembly nozzlelips is 1.0 to 4.0 times the distance between the first and second jetassembly nozzle lips.

This invention relates generally to diffusion vacuum pump apparatus andmore particularly to four-stage diffusion vacuum pump apparatus.

The operation of high vacuum diffusion pumps is generally well known. Asuitable pumping fluid (typically oil) is evaporated in a heated boilerof the pump and the resulting vapor is directed at supersonic velocitythrough a nozzle system to be condensed on a cold surface. AS the highspeed vapor stream passes between the nozzle system and the condensingsurface, it accepts by diffusion gas molecules from the chamber beingevacuated and compresses them into a higher pressure region whichnormally communicates with a mechanical backing pump. The liquidcondensate formed on the condensing surface returns to the pump boilerfor reheating and re-evaporation.

Since the conception of the vacuum diffusion pump periodic efforts havebeen made to improve such pump characteristics as pumping speed, gasthroughput capacity, attainable ultimate pressure, etc. Although someimprovelments have been made in these areas a need has continued toexist for a vacuum diffusion pump possessing significantly improvedperformance characteristics.

The object of this invention therefore is to provide a diffusion vacuumpump which exhibits significantly improved pumping performancecharacteristics.

One feature of this invention is the provision in a multi-stagediffusion vacuum pump of four vertically .stacked jet assemblies whichhave critically interrelated dimensions so as to produce in combinationhighly improved performance characteristics.

Another feature of this invention is the provision of a diffusion vacuumpump of the above featured type wherein each of the four jet assembliespossesses a uniform annular mouth gap adapted to direct pumping fluidvapor against the interior surface of the pump housing andv wherein thewidth of the second jet assembly mouth gap is 0.9-1.3 times the width ofthe bottom jet assembly mouth gap, the width of the third jet assemblymouth gap is 0.5-0.9 times the width of the bottom jet assembly mouthgap and the width of the top jet assembly mouth gap is 0.4-0.6 times thewidth of the bottom jet assembly mouth gap.

Another feature of this invention is the provision of a diffusion vacuumpump of the above featured types wherein the jet assembly mouth gaps arecircular and wherein the diameter of the second jet assembly mouth gapis 0.88- 0.92 times the diameter of the bottom jet assembly mouth gap,the diameter of the third jet assembly mouth gap is C55-0.62 times thediameter of the bottom jet assembly mouth gap and the diameter of thetop jet assembly mouth gap is 0.28-0.3 times the diameter of the bottomjet assembly mouth gap.

Another feature of this invention is the provision of a diffusion vacuumpump of the above featured types wherein the jet assemblies havesubstantially horizontal nozzle lips and wherein the distance betweenthe second and third jet assembly nozzle lips is 1.0-4.0 times thedistance between the bottom and second jet assembly nozzle lips and thedistance between the third and top jet assembly nozzle lips is 1.0-4.0times the distance between the bottom and the second jet assembly nozzlelips.

Another feature of this invention is the provision yof a diffusionvacuum pump of the next above featured types wherein each of the jetassemblies has a substantially horizontal nozzle lip and wherein thedistance between the second and third jet assembly nozzle lips is1.2-3.2 times the distance between the bottom and second jet assemblynozzle lips and the distance between the third and top jet assemblynozzle lips is between 1.7-3.7 times the distance between the bottom andsecond jet assembly nozzle lips.

These and other objects and features of this invention will become moreapparent upon a perusal of the following specification taken inconjunction with the accompanying drawing which is a partial crosssectional view of a preferred invention embodiment.

Referring now to the drawing there is shown the diffusion vacuum pump 11having a cylindrical pump housing 12. The flanged inlet aperture 13 atthe top of the pump housing 12 is adapted for connection with a vacuumchamber (not shown) to be evacuated. The fianged exhaust tubulation 14communicates with the lower portion of the pump housing 12 and isadapted for connection to a conventional mechanical forepump (notshown). The boiler section 15 located in the lower portion of the pumphousing 12 is adapted to contain a suitable pumping fiuid, for exampleoil. The hollow cooling coil 16 is attached in intimate contact with theouter surface of the pump housing 12 and is adapted for connection to asource of cooling fluid (not shown).

Resting on the bottom of the pump housing 12 and adapted to extend abovethe pumping fluid pool is the hollow cylindrical pump base 17. Supportedfrom the pump base 17 are the vertically stacked first and bottom jetassembly 21, second jet assembly 22, third jet assembly 23, and fourthand top jet assembly 24. The bottom jet assembly 21 is formed by thehollow cylindrical lower jet portion 25 which extends directly out ofthe pump base 17 and includes the central support column 26 attached byradial brackets 27. The top jet portion 28 includes the hollow cylinder30 which extends into the lower jet portion 25 and is separatedtherefrom by a uniform annular space 29. The upper jet portion 28 alsoincludes a projection 31 which extends over the upper edge of the lowerjet portion 25 and is separated therefrom by the circular mouth gap 32.The projection 31 terminates in a substantially horizontal nozzle lip 33which encircles the lower cylindrical jet portion 25. The radialmounting brackets 34 attach the upper jet portion 28 to the centralsupport column 35 which is supported by and coaxial with the centralsupport column 26.

Extending above and integral with the top jet portion 28 is the hollowcylindrical lower jet portion 36 of the second stage jet assembly 22.The upper portion 37 of the second stage jet assembly 22 is constructedand supported in the same manner as the upper portion 28 of the firststage jet assembly 21 to form the second stage mouth gap 38. Similarlythe third stage jet assembly 23 includes the top jet portion 39 whichforms the third stage mouth gap 41.

The fourth stage jet assembly 24 includes the inverted cup-shaped coverportion 42 which extends over the upper jet portion of the third stagejet assembly 24. The cover portion 42 is supported by a central columnand forms the fourth stage mouth gap 43.

During operation of the diffusion pump 11 the pumping fluid contained inthe pump boiler section is heated by a suitable heating device (notshown) and the resulting pumping fluid vapor rises through the hollowcylindrical jet assemblies. A portion of the rising vapor passes throughthe annular space 29 and is directed through the first stage mouth gap32 downwardly against the cooled interior surface of the pump housing12. This vapor condenses and returns to the pump boiler section 15.Similarly, other portions of the pumping fiuid vapor are directedagainst the inner surface of the pump housing 12 by the second stage jetassembly 22, the third stage jet assembly 23 and the fourth stage jetassembly 24. While passing between the iet assemblies and the pump wallthe high speed vapor accepts by diffusion gas molecules coming from achamber (not shown) connected for gas communication with the inletaperture 13. These gas molecules are compressed into the lower portion4of the pump housing 12 and removed through the exhaust tubulation 14 bya conventional mechanical forepump (not shown) connected thereto.

In attempting to obtain optimum performance for the diffusion pump 11 itwas found that a critical interrelationship exists between certaindimensions of the individual jet assemblies. For example, optimumperformance was obtained only if the width W2 of second stage gap 38 was0.9-1.3 times the width w1 of the first stage gap 32, the width W2 ofthe third stage gap 41 was equal to 0.5-0.9 times w1 and the width w1 ofthe fourth stage gap 43 was equal to 0.4-0.6 times w1. The` terms w1,w2, w3 and w4 represent the minimum gap widths existing between theupper and lower jet portions of the individual jet assemblies.

Similarly, it was found that the relative diameters of the jet assemblymouth gaps were extremely critical. For example, optimum performance wasobtained only with the diameter d2 of second stage jet assembly 22 equalto 0.88-0.92 times the diameter d1 of first stage jet assembly 21, thediameter d3 of the third jet assembly 23 equal to C55-0.62 times d1 andthe diameter d4 Vof the fourth stage jet assembly 24 equal to 0.28-0.3times d1.

Also found to be critical were the relative vertical distances betweenthe individual jet asemblies. Thus, for good pump performance thedistance L23 between the nozzle lips of the second stage jet assembly 22and the third stage jet assembly 23 should be between 1.0-4.0 times thedistance L12 between the nozzle lips of first stage jet assembly 21 andsecond stage iet assembly 22 and the distance L34 between the nozzlelips of the third stage jet assembly 23 and fourth stage jet assembly 24should be between 1.0-4.0 times L12. For even better pump performancethe distance L23 should be between 1.2-3.2 times L12 and L31 should bebetween 1.7-3.7 times L12.

A vacuum diffusion pump built critical range of interrelated dimensionsin accordance with the illustrated above will exhibit greatly improvedperformance characteristics. It is important to note that the criticalrange of dimension given are not limited to pumps of one size. Therelationship was found to exist for pumps of various sizes andcapacities.

Obviously, many modifications and variations of the present inventiona-re possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A diffusion vacuum pump apparatus comprising'.

a pump housing having an inlet aperture adapted to receive pumped gasand an outlet aperture adapted to exhaust pumped gas, a boiler sectionformed within said pump housing and adapted to contain a pool of pumpingfluid, a first jet assembly positioned within said pump housing abovesaid boiler section and adapted to receive a portion of the pumpingfluid vapor evaporated therefrom, a second jet assembly mounted abovesaid first jet assembly and adapted to receive a portion of the pumpingfluid vapor evaporated from said boiler section, a third jet assemblymounted above said second jet assembly and adapted to receive a portionof the pumping fiuid vapor evaporated from said boiler section, a fourthjet assembly mounted above said third jet assembly and adapted toreceive a portion of the pumping fiuid vapor evaporated from said boilersection;

each of said jet assemblies having a uniform annular mouth gap and beingadapted to direct pumping fluid vapor through said mouth gap against theinterior surface of said pump housing, the width of said second jetassembly mouth gap being 0.9-1.3 times the width of said first jetassembly mouth gap, the width of said third jet assembly mouth gap being0.5-0.9 times the width of said first jet assembly mouth gap, and thewidth of said fourth jet assembly mouth gap being 0.4-0.6 times thewidth of said first jet assembly mouth gap;

said jet assembly mouth gaps being circular and the diameter of saidsecond jet assembly mouth gap being 088-092 times the diameter of saidfirst jet assembly mouth gap, the diameter of said third jet assemblymouth gap being C55-0.62 times the diameter of said first jet assemblymouth gap, and the diameter of said fourth jet assembly mouth gap being028-03 times the diameter of said first jet assembly mouth gap; and

each of said jet assemblies having a nozzle lip, the

distance between said second and third jet .assembly nozzle lips being1.23.2 times the distance between said first and second jet assemblynozzle lips, and the distance between said third and fourth jet assemblynozzle lips being 1.7-3.7 the distance between said first and second ietassembly nozzle lips. 2. A diffusion vacuum pump apparatus comprising: apump housing having an inlet aperture adapted to receive pumped gas andan outlet aperture adapted to exhaust pumped gas, a boiler sectionformed within said pump housing Aand adapted to contain a pool ofpumping fiuid, a first jet assembly positioned Within said pump housingabove said boiler section and adapted to receive a portion of thepumping fluid vapor evaporated therefrom, a second jet assembly mountedabove said first jet assembly land adapted to receive a portion of thepumping fluid vapor evaporated from said boiler section, a third jetassembly mounted above said second jet assembly and adapted to receive aportion of the pumping fiuid vapor evaporated from said boiler section,a fourth jet assembly mounted above said third jet assembly and adaptedto receive a portion of the pumping uid vapor evaporated from saidboiler and each of said jet assemblies having a nozzle lip,

section; the distance between said second and third jet aseach of'saidjet assemblies having a uniform annular sembly nozzle lips being 1.0-4.0times the distance mouth gap and being adapted to direct pumping betweensaid first and second jet assembly nozzle fluid vapor through said mouthgap against the inte- 5 lips, and the distance between said third andfourth rior surface of said pump housing, the width of said jet assemblynozzle lips being 1.0-4.0 the distance second jet assembly mouth gapbeing 0.9-1.3 times between said rst and second jet assembly nozzle thewidth of said first jet assembly mouth gap, the lips.

Width lof said third jet assembly mouth gap being References Cited0.5-0.9 times the width of said first jet assembly mouth gap, and thewidth of said fourth jet assemlo UNITED STATES PATENTS bly gap being0.4-0.6 times the width of said tirst 2,521,345 9 /1950 Cor/[right 230101 Jefhassmbly mouth gap; 2,639,086 5/1953 Dayton 23(1 101 said Jetassembly mouth gaps being circular and the 3,165,255 1/1965 Landfors 230101 diameter of said second jet assembly mouth gap 15 3,182,895 5/1965Bchler 230 101 being 0.88-092 times the diameter of said irst jet3,273,787 9/1966 Nuer et a1 230 101 assembly mouth gap, the diameter ofsaid third jet assembly mouth gap being 055-062 times the diameter ofsaid rst jet assembly mouth gap, and the DONLEY J' STOCKING PrlmaryExammer diameter of said fourth jet assembly mouth gap 20 W. 1 KRAUSS,Assistant Examie,

being 028-03 times the diameter of said rst jet assembly mouth gap;

1. A DIFFUSION VACUUM PUMP APPARATUS COMPRISING: A PUMP HOUSING HAVINGAN INLET APERTURE ADAPTED TO RECEIVE PUMPED GAS AND AN OUTLET APERTUREADAPTED TO EXHAUST PUMPED GAS, A BOILER SECTION FORMED WITHIN SAID PUMPHOUSING AND ADAPTED TO CONTAIN A POOL OF PUMPING FLUID, A FIRST JETASSEMBLY POSITIONED WITHIN SAID PUMP HOUSING ABOVE SAID BOILER SECTIONAND ADAPTED TO RECEIVE A PORTION OF THE PUMPING FLUID VAPOR EVAPORATEDTHEREFROM, A SECOND JET ASSEMBLY MOUNTED ABOVE SAID FIRST JET ASSEMBLYAND ADAPTED TO RECEIVE A PORTION OF THE PUMPING FLUID VAPOR EVAPORATEDFROM SAID BOILER SECTION, A THIRD JET ASSEMBLY MOUNTED ABOVE SAID SECONDJET ASSEMBLY AND ADAPTED TO RECEIVE A PORTION OF THE PUMPING FLUID VAPOREVAPORATED FROM SAID BOILER SECTION, A FOURTH JET ASSEMBLY MOUNTED ABOVESAID THIRD JET ASSEMBLY AND ADAPTED TO RECEIVE A PORTION OF THE PUMPINGFLUID VAPOR EVAPORATED FROM SAID BOILER SECTION; EACH OF SAID JETASSEMBLIES HAVING A UNIFORM ANNULAR MOUTH GAP AND BEING ADAPTED TODIRECT PUMPING FLUID VAPOR THROUGH SAID MOUTH GAP AGAINST THE INTERIORSURFACE OF SAID PUMP HOUSING, THE WIDTH OF SAID SECOND JET ASSEMBLYMOUTH GAP BEING 0.9-1.3 TIMES THE WIDTH OF SAID FIRST JET ASSEMBLY MOUTHGAP, THE WIDTH OF SAID THIRD JET ASSEMBLY MOUTH GAP BEING 0.5-0.9 TIMESTHE WIDTH OF SAID FIRST JET ASSEMBLY MOUTH GAP, AND THE WIDTH OF SAIDFOURTH JET ASSEMBLY MOUTH GAP BEING 0.4-0.6 TIMES THE WIDTH OF SAIDFIRST JET ASSEMBLY MOUTH GAP; SAID JET ASSEMBLY MOUTH GAPS BEINGCIRCULAR AND THE DIAMETER OF SAID SECOND JET ASSEMBLY MOUTH GAP BEING0.88-0.92 TIMES THE DIAMETER OF SAID FIRST JET ASSEMBLY MOUTH GAP, THEDIAMETER OF SAID THIRD JET ASSEMBLY MOUTH GAP BEING 0.55-0.62 TIMES THEDIAMETER OF SAID FIRST JET ASSEMBLY MOUTH GAP, AND THE DIAMETER OF SAIDFOURTH JET ASSEMBLY MOUTH GAP BEING 0.28-0.3 TIMES THE DIAMETER OF SAIDFIRST JET ASSEMBLY MOUTH GAP; AND EACH OF SAID JET ASSEMBLIES HAVING ANOZZLE LIP, THE DISTANCE BETWEEN SAID SECOND AND THIRD JET ASSEMBLYNOZZLE LIP BEING 1.2-3.2 TIMES THE DISTANCE BETWEEN SAID FIRST ANDSECOND JET ASSEMBLY NOZZLE LIPS, AND THE DISTANCE BETWEEN SAID THIRD ANDFOURTH JET ASSEMBLY NOZZLE LIPS BEING 1.7-3.7 THE DISTANCE BETWEEN SAIDFIRST AND SECOND JET ASSEMBLY NOZZLE LIPS.